lavfi/thumbnail: add support for named options.

doc/filters.texi

@@ -5251,22 +5251,36 @@ Swap U & V plane.
 @section thumbnail
 Select the most representative frame in a given sequence of consecutive frames.
 
-It accepts as argument the frames batch size to analyze (default @var{N}=100);
-in a set of @var{N} frames, the filter will pick one of them, and then handle
-the next batch of @var{N} frames until the end.
+The filter accepts parameters as a list of @var{key}=@var{value}
+pairs, separated by ":". If the key of the first options is omitted,
+the arguments are interpreted according to the syntax
+thumbnail[=@var{n}].
+
+@table @option
+@item n
+Set the frames batch size to analyze; in a set of @var{n} frames, the filter
+will pick one of them, and then handle the next batch of @var{n} frames until
+the end. Default is @code{100}.
+@end table
 
-Since the filter keeps track of the whole frames sequence, a bigger @var{N}
+Since the filter keeps track of the whole frames sequence, a bigger @var{n}
 value will result in a higher memory usage, so a high value is not recommended.
 
-The following example extract one picture each 50 frames:
+@subsection Examples
+
+@itemize
+@item
+Extract one picture each 50 frames:
 @example
 thumbnail=50
 @end example
 
+@item
 Complete example of a thumbnail creation with @command{ffmpeg}:
 @example
 ffmpeg -i in.avi -vf thumbnail,scale=300:200 -frames:v 1 out.png
 @end example
+@end itemize
 
 @section tile
 

libavfilter/version.h

@@ -30,7 +30,7 @@
 
 #define LIBAVFILTER_VERSION_MAJOR  3
 #define LIBAVFILTER_VERSION_MINOR  48
-#define LIBAVFILTER_VERSION_MICRO 101
+#define LIBAVFILTER_VERSION_MICRO 102
 
 #define LIBAVFILTER_VERSION_INT AV_VERSION_INT(LIBAVFILTER_VERSION_MAJOR, \
                                                LIBAVFILTER_VERSION_MINOR, \

libavfilter/vf_thumbnail.c

@@ -27,6 +27,7 @@
  * @see http://notbrainsurgery.livejournal.com/29773.html
  */
 
+#include "libavutil/opt.h"
 #include "avfilter.h"
 #include "internal.h"
 
@@ -38,27 +39,27 @@ struct thumb_frame {
 };
 
 typedef struct {
+    const AVClass *class;
     int n;                      ///< current frame
     int n_frames;               ///< number of frames for analysis
     struct thumb_frame *frames; ///< the n_frames frames
     AVRational tb;              ///< copy of the input timebase to ease access
 } ThumbContext;
 
+#define OFFSET(x) offsetof(ThumbContext, x)
+#define FLAGS AV_OPT_FLAG_VIDEO_PARAM|AV_OPT_FLAG_FILTERING_PARAM
+
+static const AVOption thumbnail_options[] = {
+    { "n", "set the frames batch size", OFFSET(n_frames), AV_OPT_TYPE_INT, {.i64=100}, 2, INT_MAX, FLAGS },
+    { NULL }
+};
+
+AVFILTER_DEFINE_CLASS(thumbnail);
+
 static av_cold int init(AVFilterContext *ctx, const char *args)
 {
     ThumbContext *thumb = ctx->priv;
 
-    if (!args) {
-        thumb->n_frames = 100;
-    } else {
-        int n = sscanf(args, "%d", &thumb->n_frames);
-        if (n != 1 || thumb->n_frames < 2) {
-            thumb->n_frames = 0;
-            av_log(ctx, AV_LOG_ERROR,
-                   "Invalid number of frames specified (minimum is 2).\n");
-            return AVERROR(EINVAL);
-        }
-    }
     thumb->frames = av_calloc(thumb->n_frames, sizeof(*thumb->frames));
     if (!thumb->frames) {
         av_log(ctx, AV_LOG_ERROR,
@@ -226,6 +227,8 @@ static const AVFilterPad thumbnail_outputs[] = {
     { NULL }
 };
 
+static const char *const shorthand[] = { "n", NULL };
+
 AVFilter avfilter_vf_thumbnail = {
     .name          = "thumbnail",
     .description   = NULL_IF_CONFIG_SMALL("Select the most representative frame in a given sequence of consecutive frames."),
@@ -235,4 +238,6 @@ AVFilter avfilter_vf_thumbnail = {
     .query_formats = query_formats,
     .inputs        = thumbnail_inputs,
     .outputs       = thumbnail_outputs,
+    .priv_class    = &thumbnail_class,
+    .shorthand     = shorthand,
 };